Articles

Today economists' views on long-run economic
growth are more than usually divergent.. A minority of economists hold
to a baseline vision laid out in the 1950s which is pessimistic about how
policies might affect growth. A substantial group of economists hold to
endogenous growth perspectives, and have concluded that good and bad economic
policies can have much more significant effects because exeternalitieswedges
between the social returns realized by the economy and the private returns
realized by investorsare pervasive.

One's conclusions about the ability of
economic policies to affect economic growth depend on one's vision of economic
growth. Nevertheless there is strong reason to believe that the American
economy invests too little. And as one moves away from the baseline framework
toward endogenous growth perspectives, the case for tuning American economic
policy in the direction of generating a substantial budget surplus and
of other policies to boost national investment becomes overwhelming.
Most economists hold neither to the original baseline of the 1950s nor
to endogenous growth perspectives, but have taken up a position in the
middle. It is interesting to note that while the rhetoric of this middle
way sounds like the 1950s baseline, its substance --its conclusions about
the effects of policies on economic growth--is closer to the endogenous
growth perspective.

There is a sense in which we are all endogenous
growth theorists now.

Biography

J. Bradford DeLong is a professor of
economics at the University of California at Berkeley, a research associate
at the National Bureau of Economic Research, and the co-editor of the Journal
of Economic Perspectives. From 1993 to 1995 he was a deputy assistant
secretary for economic policy at the U.S. Department of the Treasury.

Introduction

In the 1950s and 1960s measured real GDP
per worker in the United States increased at roughly 2.5% per year; since
1970 it has averaged less than 1.0% per year. [2] This productivity slowdown
is the major macroeconomic event in the United States over the past generation.

Now measured estimates of real GDP growth
probably understate true growth in productivity because they suffer from
the standard problems of index numbers. Boskin et al. have concluded that
true growth is between half and one percentage point per year greater than
measured growth. [3] Thus true real GDP per worker growth over the past
generation has been not 1.0% per year but 2.0% per year--still a very large
number by long-run historical standards.

But the findings of Boskin et al. do not
suggest that the magnitude of the productivity slowdown is any smaller:
the American economy is still growng much more slowly than in the past.
Because have a social insurance system that makes sense only if growth
continues at its pre-1970 pace, promises made about future tax rates and
benefit levels cannot be kept. The productivity slowdown makes America
a poorer country than it might otherwise have been. And it makes American
politics less civil: fights over how to redistribute a pie perceived as
growing slowly are much more bitter than fights over how to allocate the
dividend from faster economic growth.

Can anything be done to reverse this slowdown?
This essay provides a short view of how different policies are likely to
affect economic growth. The task is complicated because economists' views
on the nature and causes of the wealth of nations are, today, more than
usually divergent.

Largely as a result of work Paul Romer,
today economists' beliefs about the nature and causes of economic growth
diverge more than is usual. [4] A substantial minority of economists today
is attached to Paul Romer's vision. Its advocates see externalitieswedges
between the social returns realized by the economy and the private returns
realized by investors everywhere: the advance of economically-useful knowledge
and thus of total factor productivity depends urgently on the progress
of other forms of investment, and is intimately tied up with monetary and
fiscal policy. Some economists work with the baseline vision of the process
of economic growth as developed by Robert Solow. [5] This vision lead to the conclusion that growth
does not depend that strongly on economic policy, for most of it is determined
by extra-economic factors: the progress of science and technology depends
little on monetary or fiscal policy. The center of American economics today
finds most attractive an extended version of Solow's framework in which
physical investment contributes a greater share of economic growth, and
in which other kinds of investment--most importantly in human capital through
education and training--are powerful sources of increased productivity.
6

An important argument of this essay is
that many advocates of the center position suffer from a degree of cognitive
dissonance: they understand their position to be that the reformulation
of the Solow framework has turned back Paul Romer's challenge, and yet
as far as implications for economic policy are concerned, Mankiw, Romer,
and Weil are far closer to perspectives usually identified with Paul Romer
than they are to those of Robert Solow.

Robert Solow's Framework

Understanding the Solow Framework

By how much would changed policies boost
economic growth? The answer to this question depends on what the underlying
determinants of economic growth are--and on which of economists' three
visions of economic growth you hold to. Each vision leads to different
conclusions about how much changed policies can boost growth.

The baseline vision of economic growth
as set out by Robert Solow begins with an aggreagate production function:
total GDP (written "Y") is a function of the economy's labor
resources L, its capital stock K, and its "technology" or total
factor productivity level A:

(2)

Using lowercase letters to denote proportional
rates of change, we can use (2) to decompose growth in output per worker
into various components:

(3)

The rate of growth of GDP per worker (y/l)
is (a) increased by a higher share of GDP devoted to investment
(I), (b) decreased by a higher rate at which the physical capital
stock depreciates (d), (c) decreased by a faster labor
force growth rate (n), and (d) increased by faster growth in
technology or total factor productivity ( t ). An
increase in the rate of growth of the technology or total factor
productivity of the economy translates one-for-one into an increase
in output per worker growth.
Equation (3) is an accounting framework. It holds by definition. It becomes
a theory of economic growth, and gains empirical content, when judgments
are made about the relationship of total factor productivity growth ( t
) to the other determinants of growth, and about the size of the parameter
( a ) that governs the impact of investment and accumulation on
GDP.

The strength of the other of these effectsthe
amount by which an increase or decrease affects GDP per worker growthdepends
on the parameter a, the share of national product that is
earned by owners of capital (rather than suppliers of labor), and on the
economy's output-to-capital ratio (Y/K).Multiply the capital share
a by the output-to-capital ratio to obtain the (gross of depreciation)
marginal product of capital:the extra boost to GDP next year produced
by a $1 boost to this year's investment.

Using the Solow Framework

For the United States today the aggregate
output-to-capital ratio and the capital share are roughly one-third and
0.3. Together these imply a (gross of depreciation) marginal product of
capital of roughly ten percent per year.Thus Robert Solow's framework tends
to produce pessimistic conclusions about the ability of anything (except
for raw improvements in technology generated by extra-economic factors)
to significantly boost economic growth. Because the parameter a
is relatively small, boosts to investment are not that effective at boosting
GDP per worker growth. 7

For example, consider a shift in the government
budget deficit that brings it into substantial surplus, a shift in fiscal
policy that boosts national savings and investment by an amount equal to
some three percent of GDP each year. Let us look at the effects of such
a policy after one year, five years, and twenty years: one year to gauge
the immediate impact; five years to approximate the decision-making horizon
of the American political system; and twenty years to gauge the long-run
impact without pushing calculated effects so far in the future that analysis
loses all credibility--twenty years is about as far as we can look into
the future without passing completely out of policy analysis and into theology.

In the Solow framework such an increase
boosts growth in the first year after the policy shift by roughly 0.28%:
at current levels, a shift of some $210 billion a year away from public
and private consumption has produced a boost to the level of GDP of $21
billion in the first year. But by the tenth year the shift to a more investment-
and capital-intensive economy has lowered the returns to capital and increased
the investment effort necessary to keep the proportionately higher capital
stock from depreciating: the benefit to growth is only 0.17%. And by the
twentieth year, the increase in economic growth is only 0.11%. In the very
long run diminishing returns set in, and the net result is not a change
in the growth rate but a permanent boost to the level of real GDP per worker
of:

(4)

where g is the growth rate of total factor
productivity, and D I is the boost to investment as a share of national
product.
Now such a shift in policy would surely have a very high social benefit-cost
ratio: the net marginal product of the extra investments made average 6.2%
per year, considerably higher than the cost of capital implied by our current
long-run real interest rates of 3% per year or so. But this creation of
a large government budget surplus is a major shift in policy: a change
in policy direction twice as large in relative terms as either the 1990
or the 1993 deficit-reduction effort. The benefits in faster economic growth
are an increase of 0.17% per year in annual growth over the next twenty
years--not overwhelmingly large by the standards of TV journalists or politicians.

Free Lunches?

Easier Monetary Policy. What of the view that the Federal Reserve is greatly
retarding the growth of the American economy--that easier monetary policy
would allow the U.S. economy to grow much, much faster?

In popular discussion this view is often
put forward roughly as follows: During the "seven fat years"
of the economic expansion of the 1980s, GDP growth in the United States
averaged 3.9% per year. Before this boom tight monetary policy by the Federal
Reserve had kept the U.S. in recession; this boom ended because tight monetary
policy by the Federal Reserve pushed the U.S. into recession. Why not simply
eliminate tight monetary policy, and grow at 3.9% per year--roughly 2.9%
per worker per year--forever?

The problem with this argument is that
much of economic growth during booms is a straightforward consequence of
lowering the rate of unemployment. When the rate of unemployment falls,
more workers join the labor force because they see that they have a better
chance of finding a good job. Holding the unemployment rate constant, a
one percentage-point increase in labor force growth over a year increases
real GDP by an estimated 0.54 percent. Even when the labor force does not
increase, a reduction in the unemployment rate is the creation of new jobs
for the economy: holding the labor force constant, a one percentage-point
decrease in the unemployment rate over a year increases real GDP by an
extra 1.67 percent.

With the labor force growing at its current
pace of approximately 1.0 percent per year and with underlying productivity
growth at its current pace, real GDP growth holding the unemployment rate
constant averages some 2.1% per year. About 1.8% per year of economic growth
during the 1980s was a result of the reduction in unemployment that takes
place during a boom.

During a boom growth is faster than average
because unemployment falls. Looser monetary policy does accelerate economic
growth by generating such a boom and such a reduction in unemployment.
But the magnitude of the productivity boost from reducing unemployment
is limited. 4% per year growth would, with the labor force expanding as
current demographics allow, lower unemployment by 1.1% per year. Four and
a half years at 4% growth would lower the U.S. unemployment rate below
zero--and at some point well before then prices would start to rise rapidly
in a spiral of renewed inflation. Figuring out how to reduce the rate of
unemployment that the economy can attain without generating rapidly-rising
inflation is an important task shared by the Federal Reserve and the Department
of Labor. But even success in lowering this non-inflation-accelerating
rate of unemployment will not lead to 4% per year growth indefinitely.
Maintaining an average non-inflationary unemployment rate of 5% rather
than 6% is certainly worth doing. But over a twenty year horizon such a
shift in the attainable rate of unemployment is an increase in average
economic growth of only 0.12% per year: not enough to be visible to politicians
or others examining the tracks of economic growth.

Better Fiscal Policy. What of the view that tax reform--relatively small
changes in the tax code--could trigger large increases in economic growth
through improvements in productive efficiency? The tax law changes in 1981's
ERTA , the flagship initiative of the Reagan administration, were designed
to have as large a positive supply-side impact as possible: every dollar
of notional revenue loss was spent reducing marginal tax rates for someone
(in sharp contrast to the 1997 tax law changes, which appear to ahve been
designed to have as small an impact on incentives as possible). Lawrence
Lindsey has produced the largest estimates of the supply-side benefits
from ERTA's tax reductions: he finds that each dollar's worth of tax cut
(defined in terms of notional static revenue loss) triggered about fifty
cents worth of additional real GDP (once you take account of the shift
from unrecorded and untaxed to recorded and taxed economic activity).8

Thus ERTAtriggered, according
to Lindsey's estimates, an increase in the real GDP growth rate of 0.3%
per year over the five years after implementation--an increase in average
real GDP growth over a twenty-year horizon of less than 0.1% per year.

Lindsey's estimates are the largest credible
estimates of supply-side effects that I Have seen. And even there the boost
to growth from a tax rate reduction one-third as large as ERTA is
on the order of 0.1 percentage point per year. One again not enough to
be visible to politicians or others examining the tracks of economic growth.

Alternative Frameworks

The Mankiw-Romer-Weil Framework

Today the modal view of economic growth--the
view that most economists who have thought long about the issue would hold--is
the view set out by Gregory Mankiw, David Romer, and David Weil. It extends
the Solow model by augmenting the production function to allow for humancapital
H, acquired through education:

(5)

Output-per-worker growth can then be written
as:

(6)

with the extra terms appearing because
growth could be produced not just by technological improvements or by investments
in physical capital, but also by increases in education: investments in
human capital.

It also extends the Solow model by allowing
for different values for the parameters that govern the returns on investments
in physical and human capital: a is estimated from international data as
roughly 0.45 or so (as opposed to 0.3 o so in the basic Solow framework).
b, the corresponding coefficient governing benefits from investments in
education, is roughly 0.25.

These differences combine to give changes
in policy significantly larger effects. The long run impact of a boost
to investment on real GDP is:

(7)

A shift in fiscal policy into surplus
that would generate a boost to private and public investment of three percentage
points worth of GDP would boost first-year economic growth by 0.43% in
the Mankiw-Romer-Weil framework (as opposed to 0.28% in the Solow framework.
Such a large policy shift would boost growth by 0.27% (as opposed to 0.11%)
by the twentieth year, for a total twenty-year increase in GDP per worker
of .34% per year--fully twice as large as in the Solow baseline.

Why the difference? First, because the
addition to the model of "education capital" slows down the approach
of diminishing returns: increases in productivity generate increases in
investment in education which produce further increases in productivity.
Second, Mankiw, Romer, and Weil's estimates of the parameters of the production
function suggest considerably larger returns to investments in physical
capital. This makes the initial impact of higher investment on growth larger,
and it also slows down the approach of diminishing returns as well.

The Endogenous Growth
Framework

The most optimistic vision of the potential
impact of policy on growth follows the path laid out by Paul Romer, and
is often referred to as "endogenous growth theory." It begins
by noting that the engine of growth is-- as Solow demonstrated in the 1950s--the
advance of economically-useful knowledge. But no one believes that advances
in economically-useful knowledge simply drop from the sky like manna from
heaven.

The Logic of Endogenous Growth. The applied science and organizational changes
that have greatly multiplied productivity have been very closely tied to
economic life. For example, after World War II continental Europe grew
rapidly, as it built its capital stock and worker skills back to pre-World
War II levels. But continental Europe did much better than simply return
to its pre-World War II growth trend: today it has output per capita levels
more than forty percent above what you would have expected from simple
extrapolations of pre-World War II or pre-World War I long-run economic
growth trends. The magnitudes of differences in economic performance across
eras for the same country and across countries in the same era cannot but
make any observer skeptical of a claim that countries must "learn
to live with" their long run growth trends. Instead, there is every
reason to think that pro-growth policies can nurtureand anti-growth policies
destroylong-term economic growth.

What would a productive set of pro-growth
policies would be? How much extra economic growth would they generate?
And how about the argument that the market system will take care of it
all anywaywon't market forces generate the "right" amount of
economic growth, and won't any additional growth come at much too high
a price in terms of reduced standards of living for those who make increased
investments in the future?

The answer is that the Invisible Hand
is very good at directing economic activity when resources are scarce,
and property rights are straightforward. But economically-useful knowledge
is not scarce in this sense: just because I am making use of a piece of
knowledge doesn't mean that you cannot use the same piece as well. The
nature of knowledge-as-commodity guarantees that it is a broad and important
area of the economy where public involvement is needed, and where reliance
on the market alone will not produce good outcomes.

The "Narrow" Version of Endogenous
Growth. Endogenous growth theory
divides into two strands of thought. One is that the principal benefits
to productivity come from investments in research and developmentthat an
additional dollar spent by the private sector on research and development
boosts GDP by between fifty cents and a dollar. 9 Investments in research and development have
enormous social returns to the economy. And private industry tends to significantly
underinvest in research and development, because the firms that undertake
the research do not reap the lion's share of the social benefits.For example, consider current computer
software human interface technology: the windows-icons-menu-pointer paradigm
for presenting organized information to knowledge workers. The work that
led to this technological breakthrough was almost all undertaken by the
Xerox Corporation, at their Palo Alto Research Center, in the 1970s. Xerox
has barely made a cent off of this advance in technology. Apple used to
make a good deal of money off of this advance in technology. Microsoftand Intel are now making an enormous amount of money off of this advance
in technology.

The net result? Large benefits to the
economy and the society in terms of expanded productivity growth from the
work carried on at Xerox's Palo Alto Research Center in the 1970s. But
barely a cent returned in revenues to Xerox from this particular drain
on its cash flow. Companies that are in business to make money will not
long spend a great time and effort on such research projects that do not
boost productivity and revenues, even if they boost industry productivity
and revenues manyfold.

Thus there is every reason to believe
that the private sector tends to underinvest in research and development:
that policies that boost research and development spending by a dollar
a year promise fifty cent or one dollar increases in annual real GDP.

This is the "narrow" flavor
of endogenous growth theory: if we could channel an additional 0.2% of
GDP into private-sector investment in research and development, we would
generate GDP per capita growth higher by between 0.1 and 0.2% per year.
Note that this is as large an increase in GDP as was generated by a $210
billion change in the annual federal budget balance according to the Solow
framwork, yet it is accomplished by simply boosting private (and public)
research and development by roughly $15 billion a year.

The "Broad" Version of Endogenous
Growth. A second strand of "endogenous
growth" theory suspects that the relationship between technology improvement
and economic activity overall is more indirect. A large share of advances
in technology have to come from "learning-by-doing": from attempting
to utilize new types and new generations of capital equipment, and figuring
out in the process of implementation how the production process needs to
be reorganized and how the capital goods need to be redesigned to produce
maximum productivity.

Still further increases in productivity
have to come with the increases in workers' "human capital" from
on-the-job training: the best way to become skilled and productive at handling
modern machine technologies is to work at applying them, and improvements
in workers' skills and capabilities are social benefits to the economy's
productivity that are usually not included in businesses' calculations
of their returns on investment. A large number of articles have proposed
a wide variety of plausible mechanisms. 10

I see a powerful case that generic investments
in machinery and equipment carry social rates of return of thirty percent
or so: boost spending on equipment by one dollar, and find that next year's
GDP is higher by thirty cents. Others disagree. It is possible that such
high boosts from equipment investment are to be found in developing countries
(where the acquisition of new machinery and equipment carries with it the
acquisition of perhaps a century's worth of technological development and
improvement) and that in advanced industrial economies the social returns
to equipment investment are merely "normal": the data make it
hard to tell. But the benefits are likely to be larger than those found
in the "narrow" version of endogenous growth theory.

What is clear is that the bulk of increases
in productivity and living standards come and always have come from advances
in knowledge and improvements in the application of knowledge, and that
it is simplistic to think that these advances in knowledge and improvements
in the application of knowledge are generated by processes unconnected
with the rest of the economy.

The "endogenous growth" theories
carry a clear lesson: boost whatever economic activities are the carriers
of advances in the application of knowledge. But what if--as in our case--we
do not know which economic activities are the carriers of true advances
in the application of knowledge? Then boost all forms of investment. In
most of the categories the boost will simply generate higher productivity
according to the market's rate of return: the economy will not gain extraordinarily;
however, it will not lose either but receive its money's worth. And in
some of the categories--those that do turn out to be crucial--the economy
will receive the significant free lunch of an increase in the rate of improvement
of economically-useful knowledge, and thus of the rate of productivity
growth.

Potential Increases in Annual Economic Growth from a 3%
Shift in Government Fiscal Balance

Model

Horizon:
1-Year

5-Year

20-Year

Solow Baseline

0.28%

0.24%

0.17%

Extended Solow

0.43%

0.40%

0.34%

Narrow Endogenous Growth

0.68%

0.56%

0.46%

Broad Endogenous Growth

0.74%

0.61%

0.53%

The table above puts the estimated gains
to economic growth according to all of the various frameworks from a policy
of fiscal surplus that succeeded in boosting investment in America by some
three percentage points of GDP or so. Such a shift in investment is a large-but-not-completely-unrealistic
possible effect of a $210 billion per year swing in the overall fiscal
balance, given the failure of domestic private saving to offset the fall
in government saving in the 1980s and given the limited ability of capital
inflows from abroad to compensate for the shortfall in domestic saving.

Implications

One important implication is that, for
all the difference in presentation, philosophy, and rhetoric between the
"endogenous growth" perspective on the one hand and the Solow
model baseline and its revisions on the other, the perspectives are not
radically distinct. At least, they are not radically distinct as far as
their predictions for output over twenty-year time spans are concerned.
Policies to boost savings and investment have effects that fall over a
considerable range, but are not totally dissimilar.

A second implication is that the central
position held by economists today, a position that in its rhetoric is close
to the original framework of Robert Solow, is in reality--in its estimates
of the effects of economic policy over a twenty year horizon--close to
the framework of Paul Romer. As neither Milton Friedman nor Richard Nixon
said, we are all endogenous growth theorists now--but this substantive
victory of the endogenous growth perspective has passed without much explicit
notice.

What view you take of the likely effectiveness
of budget and tax policies, or of subsidy and regulatory policies, at boosting
growth depends on which vision of economic growth you adoptthe standard
Solow baseline; the extensions that attribute a larger role to investment
(especially to investment in human capital through education); the "narrow"
version of endogenous growth theory that places great stress on the high
benefits from investments in research and development; or the "broad"
version of endogenous growth theory that places stress on the overall productivity
benefits from broad categories of investment.

Perhaps the best way to think about the
interaction of broad visions of economic growth and economic policy is
that broader visions of growth raise the stakes at risk with respect to
policies that move the budget into either substantial deficit or large
surplus. Deficits that boost interest rates and crowd out investment are
much worse when the investments being crowded out are investments in research
and development that not only boost the productivity of the company undertaking
them, but also boost the productivity of other firms as well).

Any shift from the Solow baseline in a
direction of more optimistic visions of economic growth would tend to lead
one to strongly support tax law changes to boost investment. As Alan Auerbach
frequently points out, a belief in large positive externalities from capital
investment strengthens the case for only certain particular kinds of tax
law changes to promote investment. To the extent that the case for tax
incentives rests on external benefits, they are external benefits from
investment, not from saving. 11

Unfortunately, it is not at clear what
the best policies to promote investment are. A desire to mitigate revenue
loss leads marginal incentives: marginal research and development tax credits;
marginal investment tax credits; and so forth. But our experience with
designing "marginal" incentives is not a good one. At some stage
the complexity of the tax code leads managers to in the most part throw
up their hands: run their business as they see fit, and after the fact
bring in consultants to figure out which tax benefits they might be able
to claim--in which cse all of the energy gone into crafting tax incentives
to boost investment has been worse than wasted.

Conclusion

Today economists' views on the nature
and causes of long-run economic growth are more than usually divergent.
A minority of economists hold to a baseline vision laid out in the 1950s
which is pessimistic about how policies might affect growth. A substantial
group of economists hold to endogenous growth perspectives, and have concluded
that good and bad economic policies can have much more significant effects
because exeternalitieswedges between the social returns realized by the
economy and the private returns realized by investors are pervasive.

One's conclusions about the ability of
economic policies to affect economic growth depend on one's vision of economic
growth. Nevertheless there is strong reason to believe that the American
economy invests too little. And as one moves away from the baseline framework
toward endogenous growth perspectives, the case for tuning American economic
policy in the direction of generating a substantial budget surplus and
of other policies to boost national investment becomes overwhelming.

Most economists hold neither to the original
baseline of the 1950s nor to endogenous growth perspectives, but have taken
up a position in the middle. It is interesting to note that while the rhetoric
of this middle way sounds like the 1950s baseline, its substance --its
conclusions about the effects of policies on economic growth--is closer
to the endogenous growth perspective.

Thus there is a sense in which we are
all endogenous growth theorists now.

A view that investment has a larger role
in boosting growth than the baseline Solow framework suggests leads in
a lot of directions other than toward policies to balance the budget and
to decrease taxes on new investment, especially investments in research
and development, and in private investments that carry new generations
of technology.

Perhaps public infrastructure has components
that truly do promise high social returns. Pure research is bound to be
underprovided if left to the private sector alone: a true public good.
A large chunk of high-technology and telecommunications investment today
appears to have a "network" character, in which case there may
be space for a substantial public role.

The urgency of a growth agenda is strengthened
by the recognition that the United States' social insurance system was
designed for the pre-1973 rapid rather than the post-1973 slow pace of
growth.Without faster long-term economic growth America's social insurance
system as we know it is unlikely to survive the next generation. Thus there
is a sense in which the stakes at risk in the task of finding policies
to spur American economic growth are larger for the left than for the right
half of the political spectrum. All have an interest in faster economic
growth: faster growth empowers the American people to better achieve their
endswhether their ends are sitting on beaches sunning themselves, raising
their children, protecting endangered species, or increasing their level
of education.

But in the absence of faster economic
growth than has been seen in the past two decades, the future of the social
insurance state is easy to read: Medicare and Social Security devour the
rest of the Great Society and the New Deal over the course of the next
generation. Two generations hence Medicare and Social Security run up against
their own budget constraints, and destroy themselves.

1I would like to thank Tim Cogley,
Barry Eichengreen, Chad Jones, Alicia Munnell, David Romer, Lawrence Summers,
Robert Waldmann, and David Wilcox for helpful discussions on this paper
and on closely related issues.. I would also like to thank Berkeley's Institute
for Business and Economic Research, the Alfred P. Sloan Foundation, and
the National Science Foundation for research support.

6. This line of argument is best exemplified
by Gregory Mankiw, David Romer, and David Weil's (1992) "Contribution
to the Empirics of Economic Growth," N. Gregory Mankiw, David Romer,
and David Weil, "A Contribution to the Empirics of Economic Growth,"
Quarterly Journal of Economics 107:2 (May 1992), pp. 407-438.